Electric control or alarm systems



1955 o. l. H. EKMAN ELECTRIC CONTROL OR ALARM SYSTEMS 2 Sheets-Sheet 1Filed May 28, 1952 mxk tw IQ INVENTOR 0% J 7% filumw BWWJWN Y: Fm

ATTORNEYS NOV. 15, 1955 L H EKMAN 74J ELECTRIC CONTROL OR ALARM SYSTEMSFiled May 28, 1952 2 Sheets-Sheet 2 /V 1/65 IN] TO United States PatentOr 2,724,105 ELECTRIC CONTROL OR ALARM SYSTEMS Olof Ingemar HaraldEkman, Stockholm, Sweden Application May 28, 1952, Serial No. 2a0,4s2

6 Claims. (Cl. 340--227) The fire alarm systems heretofore generallyused in which control wire loops with a maximum of about tenthermo-contacts per loop are individually connected to a centralapparatus with separate control and alarm relays for each loop havelately been replaced by systems in which a number of loops or all theloops are connected in series so that they form a continuous loop with agreat number of thermo contacts. By this arrangement, the costs ofmounting and operation can be considerably reduced. Particularly, thenumber of relays and the total length of the wires of the loops may bereduced while maintaining as great control as possible.

The known systems of this kind suffer, however, from drawbacks.Resistive and capacitive impedances are provided at intervals along theloop and, upon an opening of the loop by the thermo-contacts, thelocation of the break can be determined by balancing the impedance ofthe loop from the central station to the break against impedances ofknown values at the central station. With long loops, the resistance ofthe wires and the distributed capacity between the same makes itparticularly diificult to bring about a correct impedance balance of thesystem while attaining the highest reliability possible.

The object of the present invention is to overcome these drawbacks andto increase the sensitiveness of the system and make it easier tohandle.

The invention relates to control and alarm systems with thermo-contactgroups connected in series and is substantially characterized in thatbalance irnpedances are arranged at the terminals of the series to thecentral apparatus. Then it is important that such balance im pedancesare arranged at both of the terminals of the series loop to the centralapparatus.

An embodiment of a system according to the invention, mainly intendedfor a fire alarm system, is shown in the annexed drawings.

Figure 1 discloses a simplified wiring diagram of the system. Figure 2discloses a front view of a group selec tor for the system. Figure 3discloses in front view a detail of the same group selector with theappurtenant rotatable dial removed, Figure 4 discloses a side view of'the illuminating device in this group selector and Fig. 5 is asimplified diagram of a measuring bridge circuit established uponopening of a loop circuit between stations of the alarm system shown inFig. 1.

In the wiring diagram in Figure 1 only the essential elements have beenincluded, while earlier known details have been left out provided theyare of no importance for understanding the invention.

In the drawing the central station apparatus is arranged below thedash-anddot line while the loops are arranged above the said line. Theloops connected in series are connected between the four terminals Lau,Lbu, Lai and Lbi. The loop consists, in the usual manner, of a doublewire and has an a-lead and a b lead, both ends of each lead beingconnected to a battery, not shown, at the central station. In theembodiment shown, ten group fire alarm boxes (secondary fire alarmboxes) 1-10 are arranged which are provided with manually disconnectableswitches in each lead. In the group fire 2,724,105 Patented Nov. 15,1955 ice alarm boxes series resistors R2, R3 R10 are provided in thea-lead and, moreover, parallel condensers C2, c3 C10 are connectedbetween the .eads of the loops in these fire alarm boxes. The alarmloops are connected between the fire alarm boxes, only two of theseloops, S5 and S10 being shown in detail. These loops contain a number ofthermo-contacts T, the number of such contacts being adjusted to thelength of the loop and to the conditions in the premises through whichthe loop. is drawn. Some ten thermo-contacts or more can without anydifficulty be arranged in each loop.

Upon an opening of both leads a and b, either manually at one of thefire alarm boxes or automatically by a thermo-contact T in one of theloops, an alarm is sounded at the central station and the attendantconnects one or the other end of the series loop into an alternatingcurrent bridge circuit and adjusts a bank of impedances of known valuesto balance the bridge, i. e. to connect into the bridge an impedancesubstantially equal to that of the two wire line between the break andthe central station. As a check, he may then connect the other end ofthe faulty line into a similar bridge circuit.

In accordance with this invention, balance impedances are arranged inthe loop at the two terminals of the series loop at the centralapparatus. Thus, series resistors Rm and Rh are connected in the a-lead,while parallel condensers Luci and Lin are provided between the leads.The leads then are conducted to a group selector switch GSO whichcontrols the connection of the leads to the two group selectors VGS andHGS which constitute means to identify the particular fire alarm box orloop at which the leads a and b are open. In the embodiments shown,these group selectors are made as reflections of each other. 3

The group selector to the left VGS contains a ladder or chain composedof nine resistors connected in series and ten parallel condensers, thelatter connected with one terminal to contacts arranged in a circle,which can be connected and disconnected by means of a contact bar whichcan be turned by means of the knob 101 of the group selector. A slidingcontact G rests against this bar. The tenth balance resistor VSR isconnected to the chain of resistors in the group selector and isconnected in series with two individually parallel-connected balancecondensers Luc and VSC the wires of whichare connected and disconnectedby contacts 102 which, when the bar 100 is turned round, are actuated bya cam 10 on said bar.

As to the right-hand group selector conditions are en tirely analogousas is shown in the drawing The group selectors are connected to a bridgewhich contains the condensers VBCi, VBCz and Luc for the purpose ofeffecting cooperation with the left-hand group selector VGS. The bridgebranch (neutral wire) of this bridge contains the transformer VTF in thesecondary winding of which a dim glowing lamp VGL is connected. In asimilar manner the right-hand group selector HGS is connected to abridge which contains the condensers Lic,

HBCz, HBCI and in the bridge itself (neutral wire 1) the transformer HTFwith the dim glowing lamp HGL. The condenser VSC is shunted over theterminals of the left-hand group selector to the bridge and can bedisconnected by means of the contact 102. The same is the case as far asthe condenser HSC for the right-hand group selector HGS is concerned.

The condenser Luc is in an analogous manner con nected and disconnectedby means of one of the contacts 102 by turning the bar 100 the cam 103of which conmeets and disconnects the contacts 102. The condenser Lic isin the same way connected and disconnected by means of a contact 102 byturning the bar 100 of the right-hand group selector HGS.

' The system is energized by a D. C. battery and the terminals to thesaid battery are marked with and The grounding (or the connections tothe central point of the battery) are marked conventionally. A motorgenerator MG is connected to the battery with its D. C. motor part andgives off A. C. (signal current) of suitablefrequency, for example 1000cycles per second for checking the balance of one or the other of thebridge circuits which may be established by switch GSO. All theessential parts of the system are D. C.-controlled. The motor generatorMG is started by a special starting relay GSR upon an opening of theleads a and b.

The station attendant throws the switch GSO in one sense or the otherwhen an alarm is sounded to indicate an opening of the leads a and b,for example in the sense to connect the left-hand section of the openedloop into the bridge of the group selector VGS. The bridge is energizedwith alternating current from the motor-generator, and the attendantadjusts the contact bar 100 rntil the bridge is balanced by connectinginto circuit at the central station amounts of resistive and capacitiveimpedance substantial'y equal to the lumped and distributed impedancesof leads a and b from their left ends at the central station out to thebreak. At bridge balance a relay drops out to energize signal lamps inone of th" group selectors, and the position of the knob 101 at bridgebalance affords an indication of the open loop of the alarm system.

The left-hand transformer VTF is with its primarv winding connected inparalle with a re tifier V" "hi"? in turn feeds a brid e relay VBR. Theri hth ad tr former HTF is in analogous manner connected in naralle witha rectifier Hli which feeds a brid e relay HER for the right side. Thecontact to the left-hand bridge relav VBR controls the cir"uit for twosignal lamps VSL and VOL in shunt. The right-hand bridge relay HBRcontrols in the same way the circ it for two si n l amp HSL and HOL forthe ri ht side.

The shown example relates for examp'e to a series loop withfor exampleten partial loops connected in series However, in very great systems oneor more series loops each comprising several partial loops can beconnected in the way indicated by arrows at the points A.

Figures 2-4 show how the illuminating si nals at the right or the leftgroup selector are arranged. The signal lamps, for instance VSL, arearranged in a parabolic reflector 104. the radiance opening of which iscovered with a disc 105. Said disc is provided with ten holes each holecorresponding to one of the group fire alarm boxes 110. Thus, each suchhole represents a partial loop, the hole marked with 5 corresponding tothe partial loop S5 etc. The stationary disc 105 is made of anuncoloured, transparent material, for instance plastic, while the holesare entirely open or covered with uncoloured protective glasses whi"hare provided with the respective group numbers 1-10. The group selectorknob 101 is rigidly connected to a semi-transparent dial 106 which iscoloured, for instance red. A dial of red plastic is preferably used. Insaid dial a single hole 107 is provided in such a position that when theknob is turned,

' the hole 107 will successively and one at a time expose the underlyingholes in the disc 105. A colorless protective glass may be inserted inthe hole 107.

By this it is attained hat. when the signal lamps VSL are put on, thewhole dial 106 is illuminated and indicates a red signal. By turning theknob 101 the group from which the signal has been given is selected andthe group number is shown in white light against the red background.Selection is thus facilitated and mistakes are avoided.

According to the invention the system is of such a nature thatelectrical balance is effected. For this purpose the several resistorsin the ladder or chain in the re spective group selector VGS and HSS areeach m ld? equal to the correspondingly located a lead resistor R2 R10,plus the wire resistance to the center thermo contact of the loopfollowing the resistor. The resistor Rut is made as big as the resistorVSR in the left-hand group selector, the line resistor out to theresistor R111 being taken into consideration. In analogous manner theresistors HSR and Rii are made equal to each other, the line resistancebeing taken into consideration. The condensers are also balanced inanalogous manner, so that the condensers C2-C1o, as supplemented by thedistributed capacity of leads a, b out to the center of the followingloop, have the same values as the correspondingly located condensers inthe group selectors VGS and H68.

The system is also provided with line switches, fire sig nals, alarmapparatus, group fuses, fault indicators etc. in the usual manner butwhich have not been included sine they are not essential to anunderstanding of the present invention.

When an alarm or fault signal is given, the corresponding signal lamp isswitched on which indicates that the group selector switch 680 is to beshifted optionally to the right or the left. If, for example, the switchis shifted to the right, the right-hand group selector is turned untilthe group number 1-10 for one of the groups is illuminated. The alarmsignal then has been released from said group. In order to make a checkon the indicated point of the fault, the switch GSO is shifted to theleft whereafter the knob of the left-hand group selector VGS is turneduntil a group number is illuminated which number is to be the same asthat shown by the right-hand group selector. In case these numbersdiffer it means that thermo-contacts have been fused so that twodiiferent partial loops have been formed, that is, that the fire hasspread substantially. All balancing is to begin at the thermo-contactwhich is located in the centre of the respective partial loop, forexample S5. Balancing of the whole impedance, the capacitance as well asthe resistance, therefore takes place to the centre of the respectivepartial loop whereby the sensitiveness and the control are increased.

The following facts should be particularly pointed out:

Owing to the fact that balancing takes place to the centre of eachpartial loop the unbalance will be the least possible through wireimpedance (capacitance and resistance). The system therefore will to agreat extent be independent of the fact whether disconnection takesplace at the first or at the last thermocontact of the partial loop.

As the group by means of the cam 103 disconnects the base condenser Lucand Lie respectively in certain positions, for example for the groups6-10 in the embodiment shown, apercentagewise greater increase in theunbalance is obtained for the higher groups and above all for thehighest group. This involves an increased security.

The starting condensers Luci and Lic respectively are substantiallysmaller than the base condensers Luc and Lie respectively and are sofitted that a determined and equal capacity value is obtained from thecentral apparatus to the centre of the first and the last partial looprespectively.

If more shunted series loops (each containing a number of partial loopsconnected in series) are arranged the balancing onthe right side of allthe loops must be 0 mutually equal as must also be the balancing on theleft side of all the loops. The balancing on the left side preferablyequals the balancing on the right side of the same loop. that is, thebalance impedance are equal at the ends of the loop.

The neutral wire or instrument Wire of the bridge with the dim glowinglamps VGL and HGL (and their transformers VTF, HTF) and also the relaysVBR, HBR are normally current carrying owing to the normal unbalance inthe zero position of the group selector (VGS or HGS), but become currentfree when, upon an occurrence of an alarm, the group selector has beenturned to the respective group and on account thereof balance has beenob tained between one, for example the left part of the loop and thecorresponding part of the resistor-condenserchain in the (left) groupselector. Then the lamp is extinguished and the relay VBR isdisconnected. The dim glowing lamp VGL or HGL thus gives a continuousindication and glows fainter the more the group selector approaches thealarm-giving group. The relay VBR or HBR indicatesthe alarm-giving groupdirectly.

As an example of dimensioning it can be mentioned that the condensersC2C1o ought to be mutually equal with regard to size. The condensers Lucand Lie, VSfi and HSC and also the condenser connected to the con tact 1of the left-hand group selector VGS are three times as large as C2,while the balance condenser in the chain connected to the contact 0 ofthe right-hand group selector is one third as large as C2. The maximumvariation of the wire capacity in the loop leads then can be kept belowa suitable allowed value, for example 2.5% oi the whole capacity.

It should be observed that the condenser VSC is disconnected by thecontact 102 simultaneously with condenser Luc. In analogous mannercondenser I-iSC is disconnected simultaneously with condenser lie. Thecurrent path for the left-hand bridge relay passes through a normallyopen make contact on the generator start relay GSR, so that the lamp VSLnormally is extinguished. The same is the case as far as the right sideis concerned.

The balance condenser of the condenser chain of the group selector,which is connected to the contact 1 of the left-hand group selector VGSand also the balance condenser of the condenser chain of the right-handgroup selector, which is connected to the contact 0 of said groupselector have the function to efiect as great unbalance in the zeroposition of the respective group selector, that alarm is not indicatedin said position (the resting position)..

Having now described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. In a switch or alarm circuit, the combination with a pair of leadsextending adjacent each other through the area to be protected, acurrent source at a central station to which the input and the outputends of both leads are normally connected, alarm stations along saidleads and dividing the two-wire loop circuit thereof into a plurality ofserially connected partial loops, manually operable means at each alarmstation for opening said leads to initiate an alarm at said centralstation, a plurality of thermal switches in each partial loop foropening said leads when exposed to excessive temperatures, impedancemeans individual to each of said partial loops, and switch means at saidcentral station for connecting one end of said two-wire loop circuit asone arm of a Wheatstone bridge network upon an opening of said loopcircuit, of base impedances insaid leads at the input end and the outputend of said two-wire loop circuit; said base impedances each having amagnitude substantially greater than that of the impedance meansindividual to said partial loops.

2. In a control or alarm circuit, the invention as recited in claim 1,wherein said impedance means individual to each partial loop comprises aseries resistor and a shunt capacitor.

3. In a control or alarm circuit, the invention as recited in claim 1,wherein said Wheatstone bridge network includes as an adjustable balancearm a group of balance impedances, and a selector switch adjustable toconnect said balance impedances step-by-step into said balance arm; saidbalance impedances having values such that the step-by-step accumulatedvalues correspond respectively to that of said leads from the centralstation out to the centers of the correspondingly located partial loops.

4. In an electric control or alarm circuit, the combination with a loopcircuit comprising a pair of leads extending adjacent each other throughthe area to be controlled or protected, a current source at a centralstation to which the input and the output ends of both leads arenormally connected, section indicator stations along said leads anddividing the two-wire loop circuit thereof into a plurality of seriallyconnected partial loop sections, a plurality of thermal switches ineach. partial loop section for opening said leads when exposed toexcessive temperatures, impedance means in said section indicatorstations and individual to each of said section indicator stations,manually operable electrical measuring means at said central station formeasuring and indicating the number of section indicator impedance meansconnected in parallel between a station end of said leads and the pointat which they are opened, and switch means at said central station forconnecting one end of said two-wire loop circuit to said electricalmeasuring means upon an opening of said circuit.

5. In an electric control and alarm circuit, the combination with a pairof leads extending adjacent each other through the area to be controlledand protected, a current source at a central station to which the inputends and the output ends of both leads are normally connected to form atwo-wire loop circuit, section indicator stations along said leads anddividing the two-wire loop circuit thereof into a plurality of seriallyconnected partial loop sections, switches in each partial loop sectionresponsive to the feature to be controlled, said switches being operableto open said leads when exposed to an excessive deviation of saidfeature from normal, section indicator impedances connected between saidleads at said section indicator stations and individual to each of saidsection indicator stations, at least one base impedance at said centralstation, and means at said central station for determining the point insaid loop circuit at which said leads are opened by measuring theimpedance across that portion of the loop circuit between a station endthereof and the opening of said leads, said measuring means includingswitch means for disconnecting said base impedance when less than apreselected number of section indicator impedances are connected inparallel upon an opening of said two-wire loop circuit.

6. In an electric control or alarm circuit, the combination with a pairof leads extending adjacent each other through the area to be controlledor protected, a current source at a central station to which the inputand the output ends of both leads are normally connected, sectionindicator stations along said leads and dividing the twowire loopcircuit thereof into a plurality of serially connected partial loopsections, a plurality of thermal switches in each partial loop sectionfor opening said leads when exposed to excessive temperatures, impedancemeans in said section indicator stations and individual to each of saidsection indicator stations, measuring means at said central stationresponsive to and indicating the number of section indicator impedancemeans connected in parallel up to an opened partial loop section, andswitch means at said central station for connecting one end of saidtwo-wire loop circuit to said measuring means upon an opening of saidcircuit; said measuring means including duplicate networks for selectiveconnection respectively to the opposite station ends of said two-wireloop circuit, and said switch means comprising a common shaft operablein opposite directions by one single handle in accordance with themeasuring network to be connected to the opened loop circuit.

References Cited in the file of this patent UNITED STATES PATENTS1,977,121 Ekman Oct. 16, 1934 2,003,443 Henneberger June 4, 19352,028,653 Ekman Jan. 21, 1936 2,071,283 Grant Feb. 16, 1937 2,422,542Gustafsson June 17, 1947 2,428,290 Peck Sept. 30, 1947 2,556,363 Lord etal. June 12, 1951

